Biological Sciences Research Highlights

January 2014

Soil Bacterium Causes Biofuel Breakdown

SCF1 frees plant sugars in lignin for sustainable biofuels

Lignin, the tough woody polymer in the walls of plants, binds and protects cellulose that plants use for energy. Scientists at PNNL are part of a team that showed how a soil bacterium can degrade lignin, increasing its potential for use in biofuels.

Results: Biofuels made from plant
materials—also known as lignocellulosic biofuels—have promise as a source of sustainable
alternative fuels thanks to soil bacterium known as Enterobacter
lignolyticus SCF1. SCF1 degrades lignin and decomposes plant cell walls,
allowing access to the cellulose sugars that plants use for energy. However, much
remains to be learned about the processes and functions of SCF1 in breaking
down lignin for use in biofuels.

But a study recently published by a team from
the University of Massachusetts, the Joint BioEnergy Center, and Pacific
Northwest National Laboratory reveals key insights about SCF1, including that it
is the first soil bacterium to demonstrate the dual ability to degrade lignin
both as a food source and for breathing.

Why It Matters: Lignocellulose is a renewable and abundant energy source in sufficient
supply in the U.S. to make lignocellulosic biofuels sustainable and
economically feasible. Furthermore, lignocellulose is not used for food, so it
does not take food out of the supply chain. However, lignocellulose is one of
the more difficult biomass materials to break down and transform for biofuel
use. This work moves scientists one step farther toward that goal.

Methods: Using transcriptomics and proteomic techniques, the scientists observed increased growth
of SCF1 grown on media amended with lignin compared to that grown on unamended media.
They also observed that SCF1 degraded lignin in the absence of oxygen,
improving the plant material's ability to produce biofuel.

Additionally, the multi-omics approach
provided insights to lignin and its use as a terminal electron acceptor. This
study also showed that SCF1 is able to degrade lignin both as food
(assimilatory) and for breathing (dissimilatory)—the first soil bacterium to
demonstrate this dual capability.

What's Next? The
researchers plan to grow SCF1 in the presence of bacterial communities adapted
to switchgrass as the sole carbon source with and without poorly crystalline
iron as an additional terminal electron acceptor. The plan is to do these
experiments as a time course to test the hypothesis that iron supplements
improved deconstruction of lignin through more or different enzymes.

Acknowledgments:

Sponsors: This work was partially funded by the University of
Massachusetts, Amherst, and by a user award from the Environmental Molecular
Sciences Laboratory (EMSL). This work was also conducted in part by the Joint BioEnergy Institute supported by the U.S. Department of Energy Office of Biological
and Environmental Research.